Definition of devil's bit

: any of various plants with premorse rootstocks:

aor less commonlydevil's bit scabious: scabious 1;
especially: a common purple or white flowered scabious (Scabiosa succisa or Succisa pratensis) that is native to Europe but naturalized in eastern North America and that yields a blue dye from the leaves — compare woad

b: any of several New World blazing stars (such as Chamaelirium luteum, Liatris spicata, or Aletris farinosa) — compare button snakeroot, colicroot